Method and means for tying concrete



Patented Aug. 11, 1931 PATENT OFFICE WILLIAM S. HEWETT, OF MINNEAPOLIS, MINNESOTA METHOD AND MEANS FOR TYING CONCRETE Application led September 10, 1927. Serial No. 218,822.

This invention relates to method and means for preventing the cracking of concrete, when tied with steel. Features of the invention include the provision of an elastic covering for the steel tying elements to prevent bond between the concrete and steel, alongvwith means to adjust the tying elements after embedment.

It is well known that steel will resist large l0 tensile strains. It is also known that concrete will resist large compression strains, but will not resist great tensional stress without fracture. When these two materials are combined in a reinforced concrete structure, the

theory of the combination is to use steel to resist tension, and concrete to resist compression. However, concrete shrinks as it sets, and as the result of this shrinkage an initial tension isset up in the concrete and an initial compression in the steel. Therefore, when this structure is subjected to loads for which it is designed, the concrete is ruptured. A crack resulting from such rupture often exposes the reinforcing element for corrosion. Moreover. water may enter the cracks and, when submitted to sufficiently low temperatures. may expand and cause further disintegration.

This use of this invention prevents adverse 3 stresses due to shrinkage of the concrete. It prevents excessive tension, by first putting the concrete under compression and the steel under tension to such a degree that, when the structure is subjected to forces for which it is designed, the steel undergoes tensile strain only, and the concrete compression strains, only. The invention contemplates first, the coating of the steel reinforcing element with asphalt or other equivalent substance, then placing this element so that it can be adjusted after embedment. The next step is to adjust or tighten the steel tying element to give it an initial tension.

Features of the invention include the method, as well as all the details of construction for carrying out lie method.

Advantages will be set forth in the description of the drawings forming a part of this 60 application, and in said drawings Figure 1 is a view showing the device applied in the tying of a beam;

Figure 2 shows an application of the invention to the tying of a circular or cylindrical structure; and

Figure 3 is a detail side elevation further illustrating means accessible for adjusting the t 'ng element, Aafter embedment, in a cylin rical wall.

The numeral 1 represents two spaced supports which are bridged by the beam 2 composed principally of concrete and having a tying element 3 coated with asphalt 4 or coated with some equivalent material, the tying element and its coating being embedded as shown. The tying element can be held in any suitable manner to position it so that the concrete can loe poured around it. i The element in this instance is threaded at its ends as at 5 and these threaded portions have respectively engaged therewith, nuts 6 engaging against washers or equivalent devices By means of this threaded arrangement the tension can be varied or adjusted.

It will be understood that the rod is coated with elastic material before it is embedded. As the concrete hardens and shrinks it is permitted to slip or slidev or adjust itself upon the rod so that no material strain is set up inthe steel tying element.. After the concrete has hardened, the rods may be tightened to put under any desired tensile stress. Inasmuch as the rod has no bond in the concrete, it is free to expand while the concrete contracts. Knowing the properties of the materials, we may so adjust the tension of the rod that the concrete will not be subjected to tension under any given load. j

In the circular structure shown in Figure 2, the wall is represented'at 10, the tying Y element at 1l and its coating at 12. In this instance, the ends of the element 11 are threaded and a turn buckle 15 connects them as shown. In pouring the concrete, an opening 16 is formed, by coring, so that the turn buckle is accessible for adjustment after the pouring operation and after setting of the concrete. In a circular structure of concrete, for example, for the storage or conveyance of water under pressure, the wall is subjected to internal pressure acting generally in a radial direction. NVhen a pipe or wall of this character is built in the usual way, the steel is placed under compression and the concrete under tension due to shrinkage of the concrete. When internal pressure is added, the Whole wall is subjected to tension, and the concrete which was already under tension due to shrinkage, is ruptured. In the present method, the tying element and concrete are related in the usual way but the steel rods or bands or tying elements are coated, as above described for the beam structure, and are also provided with an adjusting means 15 for substantially the same purpose as described for the beam structure. After the concrete has properly set the turn buckle 15 is manipulated to put the tying element under proper tension.

It will be seen that this method Will counteract the eects of all shrinkage stresses. lVhen the present method is used, internal pressure tends to lengthen the wall giving a greater tension to the steel bands and reducing the compression of the concrete. The proper amount of initial stress to give the ands to obtain the desired result is easily computed. The amount of tension can be known if the number of threads per inch of the screw are known. Knowing the pressure to which the pipe is to be subjected the bands or tying elements may be so arranged as to avoid rupture of the concrete.

It will be understood that by the use of an asphalt coating, the bond between the concrete and steel is in one sense impositive and allows the concrete to shrink or without setting up any material adverse strains in the steel. The adjustment of the tying element Which places initial tension in the steel and initial compression in the concrete are of such magnitude that when the steel is submitted to the computed stress, due to the added load or forces, the concrete will still remain under compression, but such compression will be negligible as a. means tending to crack the concrete.

I claim as my invention:

1. A method of tying concrete which consists in coating the tying element with a substance which will prevent bonding and then pouring the concrete about the element.

2. ln combination, a tying element, having a coating of material thereabout which will prevent bonding, and concrete poured around the element.

3. A method of tying concrete which c0nsists in coating the tying clement with a substance which will prevent bonding, then securing the element for tensional adjustment, after embedment, and then disposing the concrete about the clement.

4.. ln combination, a tying element secured For tensional adjustment after embcdment, and having a coating of material thereabout 

